About 195 million people are under watches and warnings as the heat wave begins to reach peak temperatures

A dangerous and potentially deadly heatwave threatens much of the continental US, with dozens of record high temperatures both in the daytime and in the evening expected this weekend.(Drew Angerer/Getty Images)

About 195 million people are under watches and warnings as the heat wave begins to reach peak temperatures

A dangerous and potentially deadly heatwave threatens much of the continental US, with dozens of record high temperatures both in the daytime and in the evening expected this weekend.(Drew Angerer/Getty Images)

(CNN) — Peak temperatures from a potentially deadly heat wave are expected to begin Friday, and major US cities are taking special measures to prepare — with New York City declaring an emergency.

Over the next few days, more than 85% of the lower 48’s population will see temperatures above 90 degrees Fahrenheit, CNN meteorologist Dave Hennen said, and more than half will see temperatures higher than 95 degrees.

About 195 million people were under a heat watch, warning or advisory Friday morning.

The heat has the potential to break records and turn deadly as temperatures climb over the weekend all along the East Coast and through the Midwest.

East Coast

High temperatures are expected to scorch the major cities of the East Coast.

Boston, New York, Philadelphia, Baltimore and Washington will be under excessive heat warnings on Friday. That kind of warning is issued when the combination of heat and humidity is expected to make it feel like it is at least 105 degrees for a prolonged period.

Mayor Bill de Blasio has declared “a local emergency due to the extreme heat” in New York City. In an executive order that covers 9 a.m. Friday to 11:59 p.m. Sunday, the mayor is ordering office buildings100 feet or taller to raise thermostats to 78 degrees in an effort to conserve energy.He also encouraged residents to set their thermostats higher to help reduce energy use.

“We are about to enter a heat emergency, and must do all we can to keep New Yorkers safe,” said de Blasio. “The city government is limiting its energy use to reduce strain on the electrical grid, and now private office buildings will also have to do their part.”

With extreme temperatures through Sunday, the Verizon New York City Triathlon has been canceled. The organization says it’s not safe for the athletes or the spectators.

The city is opening about 500 air-conditioned “cooling centers” in public facilities. Public pools will be open an extra hour (until 8 p.m.) from Friday through Sunday, And the city will set up portable drinking fountains at busy pedestrian areas through Sunday.

Also canceled in the region: Saturday’s card of horse racing at New York’s Saratoga Race Course, and all races Saturday and Sunday at the Maryland Jockey Club in Laurel — where the heat index will reach 110 to 115.

“The health and safety of our horses and jockeys is our highest priority,” said Maryland Jockey Club President and General Manager Sal Sinatra.

Midwest

Major cities across region — including Chicago, Cincinnati, Cleveland, Detroit, Indianapolis, Minneapolis and St. Louis — are under excessive heat warnings.

Heat waves have also increased in frequency, rising from an average of two per year to six per year in the last five decades. The threat is especially pronounced in the Northeast, where “the frequency, intensity, and duration of heat waves is expected to increase” due to the climate crisis.

By 2050, the Northeast can expect approximately 650 more deaths each year because of extreme heat, the assessment found.